butter crock/bell ?

[lovemyryguy]

I bought a butter crock, and it has a water fill line.  So, my question is, as we use the butter in it, how does it stay water tight?  As the level of butter goes down in the bottom part, doesn't the water level stay the same?  And wouldn't that create a pocket of air which touches the surface of the butter?

I guess I'm confused about how to keep the butter from going rancid because in my head, it doesn't make sense.  

TIA!

[yitlan]

While there may be a pocket of air, it's otherwise airtight. Think of a tupperware container.  There's still air in there, but it's sealed.  In the summer, I just take mine out of the fridge and it softens quickly enough.  Between seasons it's nice to have it to help with soft butter!